Blackbox 4x initialization

I've bought an Openbuilds Lead 1010 about a year and a half ago. Haven't been able to put much time into it yet, but with the new diode laser I bought for it I'm wondering if it's initialization is normal. It's always given about 6 or 7 thunks when powered on with laptop attached, but when the laser's connected to it (powered separately), the laser comes on with each of those thunks too. The steppers don't move at all but they're clearly being powered on and off.
I've tried using different USB cables, two car batteries in place of the 24v supply, and 3 different Win10 laptops and it's doesn't change the behaviour.
So with no PC on, the CNC thunks once on power up. Then when the PC's booting you get the 6 or 7 thunks.
Best is if the PC is powered first and the control software is up (and it keeps the serial port from last time - not always) then you get one thunk on powering the CNC 24v supply.

So is this normal?

Thanks very much,